1. Field of the Invention
The present invention relates to a video printer for making a hard copy from an external video signal, and more particularly to a video printer which is set in either frame mode or field mode according to the kind of the video signal.
2. Related Art
A video printer for making a hard copy from a video signal such as NTSC signal, is provided with a frame mode and a field mode. In the frame mode, odd and even field data of one frame of the video data is written in frame memories, and is read out as a frame image for monitoring and printing. In the field mode, either odd field data or even field data is written in the frame memories, and is read out for monitoring or printing after being transformed into frame data by interpolation.
On the other hand, a video tape recorder (VTR) or a video camera outputs a special video signal in a special playback mode such as a stationary playback mode when the video tape is in pause and a reading head traces the same recording track on the video tape. The special video signal outputted in the stationary playback mode is added with a pseudo vertical synchronizing signal. Also a video signal outputted from a video game machine or the like is not composed of odd and even fields, but merely represents a single-field video image, in order to prevent flicker.
If the special video from the video game machine, having nonstandardized synchronizing signals, is input in the video printer set in the frame mode, the single-field data is written as frame data in the frame memory so that a bad image representing one field and lacking the other field is displayed or printed. Also the video signal having the pseudo synchronizing signal, such as input from a VTR in the stationary playback mode, cannot be properly monitored or printed by the video printer in the frame mode. This is because the number of horizontal scanning lines may be different between adjacent vertical scanning periods under some tracking conditions, and a consequent printed or displayed image may be deviated in the vertical position between the fields.